Process for forming lightweight nylon nonwoven web

ABSTRACT

A method of forming a lightweight nonwoven bonded web of nylon comprises collecting nylon filaments on a moving foraminous belt at a rate to form a web which weighs less than 1 oz/yd2, providing a vacuum beneath the belt, contacting the web while on the belt with an activating gas to lightly bond the filaments together at filament crossover points, and removing the web from the belt prior to the belt&#39;&#39;s entering an arc around a beltsupporting roller.

United States Patent Inventors Philip J. Stevenson 2624 McDowell Road;Robert P. Teulings, Hudson Road, both of Durham, NC. 27705 AssigneeMonsanto Company, St. Louis, Missouri,

a Corporation of Delaware Appl. No. 809,319 Filed Mar. 21, 1969 PatentedSept. 21, 1971 PROCESS FOR FORMING LIGHTWEIGHT NYLON NONWOVEN WEB 9Claims, 1 Drawing Fig.

US. Cl 156/306, 161/150 Int. Cl C09] 7/00 Field 01 Search... 156/306;

[56] References Cited UNITED STATES PATENTS 3,368,934 2/1968 Vosburgh,Sr 161/150 3,420,724 1/1969 Saunders... 156/306 X 3,485,428 12/1969Jackson 226/97 3,509,009 4/1970 l-lartmann 161/150 3,516,900 6/1970Mallonee et a1. 156/306 Primary Examiner-Reuben Epstein Attorneys-J.Bowen Ross, .lr., Russell E. Weinkauf and John D. Upham ABSTRACT: Amethod of forming a lightweight nonwoven bonded web of nylon comprisescollecting nylon filaments on a moving foraminous belt at a rate to forma web which weighs less than 1 oz/yd, providing a vacuum beneath thebelt, contacting the web while on the belt with an activating gas tolightly bond the filaments together at filament crossover points, andremoving the web from the belt prior to the belt's entering an arearound a belt-supporting roller.

PATENTEU SEPZI 197! mvsmons PHIL/P J. STEVENSON ROBERT P. TEULINGSATTORNEY PROCESS FOR FORMING LIGHTWEIGHT NYLON NONWOVEN WEB BACKGROUNDOF THE INVENTION 1. Field of the Invention This invention relates to anonwoven web and, more specifically, to a lightweight web which iscomprised of continuous nylon filaments being autogenously bondedtogether at a substantial number of filament crossover points.

2. Description of the Prior Art Bonded nonwoven fabrics are old in theart; however, the concept of manufacturing nonwoven webs from continuoussynthetic filaments is relatively new. It was not until the 1960 s thatprocesses were developed which were capable of attenuating freshlyextruded filaments and laying them down on a moving belt to form anonwoven web (U.S. Pat. No. 3,341,394, 3,338,992 and 3,276,944). Thesepatents deal primarily with polyester and polyolefinic filamentsalthough the use of nylon filaments is casually mentioned. Bonding isaccomplished by heat, solvents or adhesives. The reason continuousfilament nylon webs are only referred to in the mentioned patents and inthe prior art is that nylon is not readily bondable by these techniques.While nylon is a thermoplastic, heating nylon filaments to the meltingpoints destroys substantially all molecular orientation thus weakeningthe filament to the point of uselessness. Solvent bonding of nylonfilaments is impractical since the solvating rate is uncontrollable. Theuse of adhesive binders renders the resulting fabrics too boardy to beof any practical value.

In producing light weight webs, the use of adhesive binders to form thebonded web is further not practical because the weight of the adhesivewhich is generally about 40 percent of the total fabric weight replacesthe equivalent weight of filaments thus leaving the web with too fewfilaments to provide adequate strength. The use of solvents for bondingtends to destroy the web for the bonding rate is uncontrollable. Ineither case, the web would be subjected to a liquid or water treatmentbath which would destroy the web geometry since the web does not havethe integrity to withstand the liquid.

In the manufacture of lightweight nonwoven webs, i.e., webs weighingless than 1 oz./yd. the technique to date has been either to depositolefinic fibrous materials on a belt with bonding being carried out by aheat process or by means of depositing submicron organic fibrils onto acollection surface as set forth in U.S. Department of Commerce, Officeof Technical Services, publication number PB] 1 1437. While nonwovenfabrics can be made from nylon in accordance with the publication, thefibers are not continuous and the resulting web has little strength.

SUMMARY OF THE INVENTION In its broadest aspects, the present inventioncomprehends the formation of a nonwoven web weighing less than 1 oz./yd.and being comprised on continuous filament nylon preferably of less thandenier per filament with the filaments being autogenously bondedtogether at a substantial number of filament crossover points. Thefilaments comprising the web may be arranged in an orderless manner,that is, without any preferred orientation or they may bedirectionalized especially in the machine direction in order to build upstrength therealong.

Autogenous bonding of nylon filaments can be accomplished in accordancewith the method set forth in U.S. Pat. No. 3,516,900 filed June 17,1968, by William C. Mallonee et al. By autogenous bonding, it is meantthat bonds are formed between touching filaments without visible polymermigration at the bond points and in the absence of external bondingagents. As disclosed in detail in the above-identified application,gaseous hydrogen chloride or like activating gases contacts and isabsorbed by the nylon filaments at least along the surfaces thereof. Thehydrogen chloride molecule in the nylon causes the interchain hydrogenbonds which exist between adjacent amide groups to break and uponremoval or desorption of the hydrogen chloride from the nylon, theinterchain hydrogen bonds reform, some of which reform between amidegroups of different filaments (at crossover points) to form bondstherebetween.

In reference to the process for forming the lightweight nonwoven nylonwebs of this invention, the general procedure is set forth in U.S. Pat.No. 3,542,615 filed June 16, 1967 by EJ. Dobo et a1. However,lightweight webs must be handled more delicately than the webs of thementioned application or the prior art. The webs of this inventionshould be lifted from the belt while the belt is flat or planar andprior to the belt 5 entering an arc around a belt-supporting roller.Such a procedure prevents the web filaments from following the beltaround the roller and furthermore prevents the web filaments from beingtrapped between the foraminous collection belt and the roller. In orderthat the web has sufficient strength to maintain its integrity whilebeing lifted from the belt, the web is prepressed while moving along thebelt by means of aligned rolls or is contacted with a small amount ofthe activating gas while it remains on the belt so as to lightly bondselected touching filaments.

Therefore, an object of this invention is to provide a lightweightnonwoven bonded nylon web.

Another object of this invention is to provide a nonwoven web weighingless than 1 oz./yd. which is comprised of continuous nylon filamentsdirectionalized during laydown which are bonded together at asubstantial number of filament crossover points.

A further object is to provide a process for forming a nonwoven webweighing less than 1 oz./yd. and being comprised of continuous filamentnylon.

A still further object is to provide a lightweight nonwoven webcomprised of continuous nylon filaments being au togenously bondedtogether at a substantial number of filament crossover points.

Other objects and advantages of the present invention and their means ofattainment will be apparent from the following description andaccompanyingdrawing.

DESCRIPTION OF THE DRAWING The figure is a schematic diagram of theapparatus used for making the lightweight nonwoven web of this inventionand for carrying out the process of this invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT With reference to theFigure, extruder 10 is of the general type used for spinning continuousnylon filaments l1. Filaments 1] are drawn downwardly and attenuated byaspirator l2. Aspirator 12 forwards filaments l1 downwardly toward thelaydown zone by means of compressed air which is fed into aspirator 12by a supply line (not shown).

The laydown zone is comprised of an endless foraminous belt 14 which issupported and moved along a defined path by rollers 15 and 16, one ofwhich is positively driven. While the particular path assumed by belt 14may be varied, it is contemplated that such path will include at leastone planar surface which is to receive filaments l1 forwarded to it bymeans of aspirator 12. The planar surface is to include the area atwhich filaments 11 are deposited on belt 14 and the location at whichfilaments 11 in the form of web 17 are lifted from belt 14. Whilecertain undulations along that length are permissible, web 17 must belifted from belt 14 prior to the portion of belt 14 which carries web 17reaching roller 16 and assuming the arcuated path therearound. Thelaydown zone also includes vacuum source 18 which is in the shape of anopenended box and has exhaust means 19. Vacuum source 18 is positioneddirectly beneath aspirator l2 and below belt 14 so as to maintainfilaments 11 on belt 14 upon the deposition of the same. The length ofvacuum source 18 in the direction of roller 16 should be sufficient tofirmly position the filaments on belt 14. Depending upon the operatingconditions, a

second vacuum source of reduced suction (not shown) may be Tenacity -l-1 desirable which would be located substantially adjacent 48 Tonguetear (lbs) 0.19 vacuum source 18 in the direction of roller 16. weigh,(Dz/yd." M 8 ln order that web 17 has the integrity to withstand thetension required to lift it from belt 14 at a second location which canbe said to be included along the planar surface, web 17 EXAMPLE and {hatP of belt 14 supporting the web y be Passed The procedure as set forthin example I was followed with a P of Press mus and winch compact web 17the exception that nylon 6,6 flake was extruded. Web properand increasefilament cohesion. Alternatively, web 17 may be ties were as f lllightly bonded by means of an activating gas applicator 22 which directsan activating gas such as hydrogen chloride into web 17. Sufficientbonding will occur at filament crossover Thickness (mils) 4.4 pointsallow the web to be lifted from belt 14. While only one Density (8 [cma) 0408 of these web takeoff aiding methods is generally required, it isBending law}, (in) 1,0 possible that more than one may be desired. Suchan occasion Tenacity (lbs./i'n./oz.lyd.) 5.8 may arise when the relativehumidity is extremely low thus 58 kin it difficult for an staticelectric char e on the fila- Tang mambs') ma g Y 8 Weight (ca/yd?) 0.26ments to be dissipated.

Web 17 is lifted from belt 14 at a second location by means of a guidebar 24, is passed over guide bar 24 and is passed EXAMPLE Iv throughrolls 26 and 27 whlch forwards web 17 cage The procedure as set forth inexample 1 was followed and 29. While in gas cage 29, the nylon filamentscomprising web the resulting web properties were: 17 absorbs thehydrogen chloride gas or come like activating gas. Web 17 is thenremoved from gas cage 29 by means of guide rolls 30 and 31 and is passedthrough a heater 34 where g desorption is effected and as a resultpermanent bonding ocf g Aft d t. b 17 d ll Density (g./cm. 0.l2 curs. eresorp 10', we is rawn over gui e r0 5 Bending (m) 0.9 and 37 whereuponit proceeds to an appropriate take up Tenacity (lbs/inJoL/yd?) 6.6mechanism (not shown). If required additional gas desorption 30Elongation (i 46 ongue tear s.) can be achieved by a subsequent waterwash. weigh! (CL/yd?) 0'30 EXAMPLE] Nylon 6 flake was extruded through a14 hole spinnerette, EXAMPLE v at a rate of 2.6 g./min. Tworeciprocating aspirators were used Th procedure as Set f h i example 1was f ll d d which were supplied compressed air having an input pressureh resulting b properties were; of 64 p.s.i.g. The aspirators attenuatedthe filaments to a finished denier of from 2.0 to 2.5 and werepositioned about 16 inches above the foraminous belt. The belt speed was8.6 bk 5 0 ft./min. and the weight of the web deposited on the belt wasL I' Z L ,L J 0.09 oz./yd. The unbonded web was pressed by a pair ofBending lengthfins.) 1.0 prepress rolls while remaining on the belt.Ambient conditions 'lenacit (llzginjozJydfj 2,5

o ongation during web laydown were 76 F. and a relative humidity of 40Tongue ear (um 0.80 P 5 Weight (ca/yd?) 0.41 The web was lifted from thebelt by means of being pulled 4 over a lift bar and was passed through agas chamber filled with gaseous hydrogen chloride. After being exposedto the EXAMPLE VI gaseous hydrogen chloride for approximately 6 Secondsthe The procedure as set forth in example I was followed and web waspassed through a heated area which was comprised of the resulting webproperties were; two opposed Fostoria heat lamps where the hydrogenchloride having been absorbed by the nylon filaments was desorbed. Theweb was exposed for 25 seconds to a temperature in ex- Th, k 1 cess of200 F. The heat treatment reduced the hydrogen f g ilfigfi g chloridecontent in the web to a residual level of about 0.2 Bendinglenglh(in5 1percent by weight. Tenacity (lbsJinJozJyd) 1 L2 The web properties areas follows: Emgam" Tongue tear (lbs) 2.00 Weight (ozlyd?) 0.75

Thickness (mils) 2.0 Density (g-lcmfl 0.06 By certain processmodifications the filaments comprising f the webs of this invention canbe directionalized so that the Tenacity (lbsJinJOL/yd?) 5.0 Elongadon 45webs have greater strength, for example, in the machine Tonguetear(lbs.) 0.|2 direction than in the transverse direction. A web havingdifferential strengths find utility where tension is applied in onlyEXAMPLE ZLZfiifiiilififli Ll? 21 .3%; "123.1113226 1123353)? Theprocedure as set forth in example I was followed with a savings in webweight or a stronger web per unit weight can the exception that nylon6,6 flake was extruded. Web properbe in by rr nging most of thefilaments in the i were as f ll preferred direction so that they becomethe load-bearing members.

While any one of several methods may be used to compare the strengths inthe given directions, the preferred method is a Thickness (mils) 4.2Density 16mg) I 006 correlation between the zero span tenacities of thetwo Bending length n. 0,5 directions. In zero span tenacity, themeasured rupture load is dependent upon the component filament strengthand filament orientation only since opposed clamps which receive thefabric are positioned adjacent each other and are pulled in oppositedirections to rupture the web. It has been found that the ratio of thezero span tenacity in the high strength direction to the zero spantenacity in low strength direction (DH/DL) generally should be at least1.50 for there to be useful realization of the unidirectional strengthcharacteristics of the web.

EXAMPLE VII The general procedure as set forth in example I was followedwith the exception that nylon 6.6 was used and aspirator 12 was slopedat an angle of 30 from the vertical in the machine direction.Spinnerette l0 and aspirator 12 were positioned to direct filaments 11onto belt 14 in the area above vacuum source 18. By sloping aspiratorl2, filaments 11 were laid on belt 14 with the preferred orientationbeing in the machine direction. The resulting web properties were:

1. A process for producing a lightweight nonwoven web of continuousnylon filaments comprising the steps of:

a. forwarding a plurality of said nylon filaments toward a laydown zone,said laydown zone including a foraminous belt moving along an endlesspath, said belt being planar for a given length along said path;

b. collecting said filaments onsaid belt at a first location along saidplanar length to form a web having a weight being less than 1 oz./yd.

c. including a vacuum beneath said planar length to maintain saidfilaments on said belt during and subsequent to collection;

d. contacting said web while on said belt with an activating gas tolightly bond said filaments together at selected filament crossoverpoints whereby web integrity is increased; and

e. removing said web from said belt at a second location along saidplanar length.

2. The process of claim 1 wherein said filaments are autogenously bondedtogether at a substantial number of filament crossover points.

3. The process of claim 2 wherein said autogenously bonding saidfilaments include the steps of subjecting said web to an activating gas,said gas being at least partially absorbed by said filaments anddesorbing said gas from said filaments to permanently bond saidfilaments together at a substantial number of said crossover points.

4. The process of claim 3 wherein said desorbing is substantiallycompleted by subjecting said web to heat.

5. The process of claim 4 wherein said web is calendered while on saidbelt prior to said web removal by means of press rolls spaced inalignment on either side of said belt.

6. The process of claim 5 wherein said filaments of said web are lightlybonded together at selected filament crossover points prior to said webremoval from said belt.

7. The process of claim 4 wherein said filaments are less than 10 dpf.

8. The process of claim 4 wherein said filaments are preferentiallyarranged in a first selected direction within said fabric to increasethe fabric tenacity in said first selected direction relative a secondselected direction.

9. The process of claim 8 wherein the ratio of said first selecteddirection tenacity to said second selected direction tenacity is greaterthan 1.50.

2. The process of claim 1 wherein said filaments are autogenously bondedtogether at a substantial number of filament crossover points.
 3. Theprocess of claim 2 wherein said autogenously bonding said filamentsinclude the steps of subjecting said web to an activating gas, said gasbeing at least partially absorbed by said filaments and desorbing saidgas from said filaments to permanently bond said filaments together at asubstantial number of said crossover points.
 4. The process of claim 3wherein said desorbing is substantially completed by subjecting said webto heat.
 5. The process of claim 4 wherein said web is calendered whileon said belt prior to said web removal by means of press rolls spaced inalignment on either side of said belt.
 6. The process of claim 4 whereinsaid filaments of said web are lightly bonded together at selectedfilament crossover points prior to said web removal from said belt. 7.The process of claim 4 wherein said filaments are less than 10 dpf. 8.The process of claim 4 wherein said filaments are preferentiallyarranged in a first selected direction within said fabric to increasethe fabric tenacity in said first selected direction relative a secondselected direction.
 9. The process of claim 8 wherein the ratio of saidfirst selected direction tenacity to said second selected directiontenacity is greater than 1.50.